Comment 17 for bug 1918427

Attached is a patch for curtin that works for me, though it could use some cleanup. It installs flash-kernel in the same place GRUB gets installed for EFI-based systems, which seems like the appropriate place. Before installint it, it diverts /usr/sbin/flash-kernel so that flash-kernel's postinst doesn't try (and fail) to flash a kernel that isn't yet installed. There's existing code in enable_update_initramfs() that will undo this diversion. I suspect we should refactor disable_update_initramfs() somehow instead of duplicating this code like I've done here.

I've tested this w/ a locally-hacked squash image that has flash-kernel purged and a PPA kernel that allows grub-efi-arm64 to satisfy the bootloader Recommends. On an EFI-based system, flash-kernel never gets installed. On a Moonshot m400, flash-kernel gets installed as expected.

Once curtin has been updated with a fix like this, and MAAS has been refreshed to include it, I think we should then be able to remove flash-kernel from the arm64 cloud images.